如何制作圆角的SDL2窗口？

#include <SDL2/SDL.h>

int main(int argc, char* argv[]) {
    SDL_Init(SDL_INIT_VIDEO);

    SDL_Window* window = SDL_CreateWindow("SDL2 Rounded Window", SDL_WINDOWPOS_UNDEFINED, SDL_WINDOWPOS_UNDEFINED, 800, 600, 0);
    SDL_Renderer* renderer = SDL_CreateRenderer(window, -1, SDL_RENDERER_ACCELERATED);
    SDL_Texture* texture = SDL_CreateTexture(renderer, SDL_PIXELFORMAT_RGBA8888, SDL_TEXTUREACCESS_TARGET, 800, 600);

    SDL_Event event;
    int quit = 0;

    while (!quit) {
        while (SDL_PollEvent(&event)) {
            if (event.type == SDL_QUIT) {
                quit = 1;
            }
        }

        SDL_SetRenderTarget(renderer, texture);
        SDL_SetRenderDrawColor(renderer, 255, 255, 255, 255);
        SDL_RenderClear(renderer);

        // 绘制圆角矩形
        SDL_SetRenderDrawColor(renderer, 0, 0, 0, 255);
        SDL_Rect rect = { 100, 100, 400, 300 };
        int radius = 20;
        int x, y, p;
        x = 0;
        y = radius;
        p = 3 - 2 * radius;
        while (x <= y) {
            SDL_RenderDrawPoint(renderer, rect.x + radius + x, rect.y + radius + y);
            SDL_RenderDrawPoint(renderer, rect.x + radius + y, rect.y + radius + x);
            SDL_RenderDrawPoint(renderer, rect.x + radius - x, rect.y + radius + y);
            SDL_RenderDrawPoint(renderer, rect.x + radius - y, rect.y + radius + x);
            SDL_RenderDrawPoint(renderer, rect.x + radius + x, rect.y + radius - y);
            SDL_RenderDrawPoint(renderer, rect.x + radius + y, rect.y + radius - x);
            SDL_RenderDrawPoint(renderer, rect.x + radius - x, rect.y + radius - y);
            SDL_RenderDrawPoint(renderer, rect.x + radius - y, rect.y + radius - x);
            if (p < 0) {
                p += 4 * x + 6;
            } else {
                p += 4 * (x - y) + 10;
                y--;
            }
            x++;
        }
        SDL_RenderFillRect(renderer, &rect);

        SDL_SetRenderTarget(renderer, NULL);
        SDL_RenderCopy(renderer, texture, NULL, NULL);
        SDL_RenderPresent(renderer);
    }

    SDL_DestroyTexture(texture);
    SDL_DestroyRenderer(renderer);
    SDL_DestroyWindow(window);
    SDL_Quit();

    return 0;
}